What will I lose when I sync my iphone with a new computer?

I need to make sure that I don't lose my notes, contacts, voice memos, music, message data, app data, etc., but I've heard nasty things about first time syncing. Is there a program out there to copy stuff over, or do I just need to know how to use the settings correctly?

Thanks so much if possible!

Nothing happens

Everything, it ll be completely reset

Pravin is right.

Your iPhone's Virginity